1. Field of the Invention
The invention relates to a method for producing a self-supporting thick-film structure on a substrate over a recess in this substrate.
2. Description of the Related Art
Thick-film circuits are preferably produced on ceramic, plate-like substrates by means of printing on a paste whose active material comprises metal powders, glass and glass-ceramic powders or mixtures of glass and metal oxides. Subsequent to firing these printed-on pastes at temperatures around approximately 850.degree. C., metallic layers, glass and glass-ceramic layers or resistance layers are produced, depending on the pastes used in each case. The entire surface of these layers bonds during firing with the surface of the substrate on which they subsequently form a firmly adhering substance.
These types of thick-film circuits find application in many fields of technology.
Some cases require that the layer including the active substance does not contact the entire substrate surface, but that bulging creates cavities in which, for example, conductor paths, elevations or other circuit components are arranged. Attention is directed, for example, to DE-OS (German Unexamined Published Patent Application) DE-OS 3,015,356, DE-OS 3,008,572 and DE-OS 2,829,195. However, these closed bubbles have the disadvantage that the air cushion in the bubble has certain undesirable effects on the circuit and the circuit components. Thus, a heat flow which still occurs through the air cushion worsens, for example, the dynamic characteristics of a sensor inside the closed bubble. This is why it might be desirable in some cases that, although a cavity is formed, this cavity not be closed on all sides. In that case, a recess, through which the cavity remains open, would need to be present in the substrate, with the cavity itself, however, being covered by the thick-film structure.